Machine and method for high vacuum controlled ramping curing furnace for sog planarization

ABSTRACT

An apparatus is described for vacuum degassing and curing a spin-on-glass layer on an article. The machine has a chamber into which an article, such as at least one or more semiconductor wafers are moved by appropriate means. Means are provided for causing the chamber to be evacuated and for continuing to maintain the vacuum at less than about 100 mtorr. The temperature of the article is maintained at a substantially constant level within a first range of temperature by appropriate means during the vacuum degassing. Means are provided to ramping the temperature at a controlled rate from the first range of temperature up to the desired second range of temperature for curing of the spin-on-glass layer. The temperature of the article is maintained at a substantially constant level within the second range of temperature by suitable means for the curing. Means are provided to allow a constant inert gas flow to fill the chamber under the vacuum conditions during the operation. Means are provided for cooling the chamber and the article.

This application is a division of U.S. Ser. No. 07/618,199 filed on Nov.19, 1990, now U.S. Pat. No. 5,106,787.

RELATED APPLICATION

(1) U.S. patent application Ser. No. 07/512,401 filed Apr. 19, 1990 bythe same inventor Daniel L. W. Yen. U.S. (2) U.S. patent applicationSer. No. 07/615,377 filed by the same inventor Daniel L. W. Yen.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The invention relates to a machine and method for vacuum degassing,controlled ramping to the curing temperature, and curing of aspin-on-glass (SOG) planarization layer for an integrated circuitdevice.

(2) Description of the Prior Art

The growing and regrowing of insulating films such as silicon dioxideand the use of polysilicon and/or metals in the form of conductors,ohmic contacts, resistors and the like in the manufacture of integratedcircuits cause irregular or substantially non-planar surfaces across thesurface of the semiconductor substrate. A major problem that is causedby these irregular or non-planar surfaces is loss of resolution in thelithographic masking processed. For example, metal conductors formed onthe insulating films have different widths across the surface of thesemiconductor body due to the different resist development because ofthe resolution problems. To prevent conductors from having varyingwidths to the point where they might cause short circuits, extra spacingor tolerances are required with each conductor. The increased tolerancesreduce the number of devices that may be formed in the semiconductorstructure. This problem increases with each higher level of metallurgyand with the use of submicron lithography features. In these highlydense, submicron integrated circuits 3 or 4 levels of interconnectionmetallury is required.

These problems have been recognized in the prior art and attempts havebeen made to overcome these topographical problems principally in theone micron and above feature dimensions. These techniques can begenerally grouped in categories of planarization either involvingetchback or nonetchback techniques. Examples of such processes are shownin the S. Morimoto U.S. Pat. No. 4,721,548; W. I. Lehrer U.S. Pat. No.4,619,839; J. K. Chu et al. U.S. Pat. No. 4,775,550; V. W. Ryan et alU.S. Pat. No. 4,826,709 and C. T. Ting et al. U.S. Pat. No. 4,885,262.

The copending patent applications Ser. No. 07/512,401 now U.S. Pat. No.5,003,062 entitled "Semiconductor Planarization Process for SubmicronDevices" and Ser. No. 07/615,377 entitled "Planarization Process for ICSubmicron Devices" By Daniel L. W. Yen the same author of the presentinvention describe methods to overcome the problems involving outgassingin the nonetchback type of planarization process for both silicate andsiloxane type of spin-on-glass types of materials. These new inventionshave made it necessary to design and develop a new machine and methodfor high vacuum, controlled ramping curing furnace which allowssuccessful vacuum degassing and curing of a spin-on-glass layer withinthe same machine.

It is therefore a primary object of this invention to provide a machineand method for a high vacuum, controlled ramping vacuum degassing andcuring of a spin-on-glass layer to complete the planarization of anintegrated circuit device.

SUMMARY OF THE INVENTION

In accordance with the present invention, an apparatus is described forvacuum degassing and curing a spin-on-glass layer on an article. Themachine has a chamber into which an article, such as at least one ormore semiconductor wafers are moved by appropriate means. Means areprovided for causing the chamber to be evacuated and for continuing tomaintain the vacuum at less than about 100 mtorr. The temperature of thearticle is maintained at a substantially constant level within a firstrange of temperature by appropriate means during the vacuum degassing.Means are provided to ramping the temperature at a controlled rate fromthe first range of temperature up to the desired second range oftemperature for curing of the spin-on-glass layer. The temperature ofthe article is maintained at a substantially constant level within thesecond range of temperature by suitable means for the curing. Means areprovided to allow a constant inert gas flow to fill the chamber underthe vacuum conditions during the operation. Means are provided forcooling the chamber and the article.

Further in accordance with the invention, a method for vacuum degassingand curing a spin-on-glass layer on a integrated circuit wafer is shown.A chamber is provided. At least one wafer is moved into the chamber tobe subjected to vacuum degassing and curing. A vacuum of less than about100 mtorr. is provided in the chamber. The temperature of said wafer ismaintained at a substantially constant level within a first range oftemperature between about 250° to 350° C., during the vacuum degassing.The temperature is ramped at a controlled rate from the first range oftemperature up to the desired second range of temperature for thedesired curing. The temperature of wafer is maintained at asubstantially constant level within the second range of temperaturebetween about 350° to 500° C. during the curing step. A constant inertgas flow is provided to fill the chamber under the vacuum conditionsduring operations. The chamber and the wafer are then cooled to roomtemperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing show the following.

FIG. 1 graphically illustrates the operation of the vacuum degassing andcuring apparatus of the present invention.

FIG. 2 schematically illustrate the construction and method of operationof the vacuum degassing and curing apparatus of the invention.

FIG. 3 graphically illustrates the vacuum used during the operation ofthe vacuum degassing and curing apparatus of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The spin-on-glass materials and how they are processed are critical tothe success of the process for planarization of integrated circuits asdescribed in the above cited pending Patent Applications of Daniel L. W.Yen. The most useful materials are silicates-Si (OH)₄ andsiloxanes-(RO)nSi(OH)_(4-n). These types of materials are generallyknown and available examples of the silicate type is OCD Type 2 made byTokyo Okha Corp. and siloxane type is OCD Type 6 made by Tokyo OkhaCorp. Each spin-on-glass coating is less than about 0.3 micrometers andpreferably between about 0.08 and 0.2 micrometers. The more coatingsthat are used, the better the planarity. The material to be applied isthoroughly mixed in a suitable solvent which is usually a combination ofa high boiling point solvent and a low boiling point solvent.

The preferred low boiling point solvents are methanol, ethanol, andpropanol. The middle boiling point solvents are buthanol, penthanol,hexanol and methyl celloslve. The high boiling point solvents are butylcellosolve, propylene glycol, diethylene glycol and Carbindol. Otherpotential vehicles or solvents are NMP, HMPA, N,N-dimethylacetoamide,acetyl acetone, and malonic acid diethylester and the like.

The spin-on-glass material suspended in the vehicle or solvent isdeposited onto the semiconductor wafer surface and uniformly spreadthereover by the action of spinning the wafer. The material fills theindentations in the integrated circuit wafer surface, that isplanarization. Most of the vehicle or solvent is driven off by a lowtemperature baking step. At this point, the critical vacuum degassingstep is accomplished by subjecting the wafer to a vacuum of less thanabout 100 mtorr and 350 degrees C. This last step removes chemicalmaterials which could during latter processing cause cracking andcorrosion of the next level conductor material. Other coatings of thespin-on-glass material are applied, baked and vacuum degassed until thedesired spin-on-glass layer is formed.

The final step in the making of the spin-on-glass layer is curing.Curing is a high temperature heating step to cause the breakdown of thesilicate or siloxane material to a silicon dioxide like cross linkedmaterial. Water in the form of steam is the major reaction product ofthis reaction. The silicate spin-on-glass is cured at about 390 degreesC. and siloxane spin-on-glass is cured at about 450 degrees C. innitrogen.

Referring now more particularly to FIG. 1, there is shown the operationof the vacuum degassing and curing steps of the apparatus of theinvention. FIG. 2 schematically shows the apparatus 24 itself. Articles,such as semiconductor wafers having a planarizing spin-on-glass layerthereon are carried to the apparatus in a cassette 20. One or many ofthese wafers may be carried in this cassette 20. Conventionalmechanizisms unload these wafers within the apparatus and load them intothe furnace quartz boat 28 as is seen loaded with wafers and located inthe chamber 26 of the apparatus 24 in the FIG. 2. A vacuum pump 30,associated piping and other equipment are connected to the chamber 26 toprovide a vacuum of less than about 100 mtorr. in the chamber. Means 32are provided for heating the chamber. Other control means (not shown)are provide for maintaining the temperature of the wafer in the chamberat a substantially constant level within a first range of temperatureduring the vacuum degassing. This control means also allows ramping thetemperature of at a controlled rate from the first range of temperatureup to the desired second range of temperature for the curing step. Thiscontrol means then maintains the temperature of the wafer and chamber ata substantially constant level within the second range of temperatureduring this curing step. Means, including valves, piping and controls 34provide a constant inert gas flow to fill the chamber 26 under thevacuum conditions during operation. Cooling means are provided to coolthe chamber and wafer to room temperature. The cooling can be done byeither use of cooling water through the heat exchange structure or byusing a gas such as Helium passing through the gas heat exchanger.

The operation of the apparatus 24 may be better seen with reference tothe FIG. 1 which shoes the graphical representation in time versustemperature to which the apparatus operates. Also, the FIG. 3 shows thegraphical representation in time versus vacuum to which the apparatusoperates. After the wafer(s) each with a spin-on-glass layer thereon andwhich have been baked are described above to remove the vehicle, arepositioned in the chamber the process may begin.

The vacuum pump is turned on and the vacuum in the chamber 26 is made,for example by the FIG. 3 graphical representation. In any case it isnecessary to have an efficient vacuum system that is able to pull thevacuum of less than about 100 mTorr. and preferably less than 10 mtorr.in less than about 30 minutes as is shown in FIG. 3. During this timethe heating means 32 together with its associated control means operateto bring the temperature into the first range of temperature for vacuumdegassing of the spin-on-glass layer on each wafer. This preferred rangeis between about 250° to 350° C. This temperature range is sufficient toremove the trapped gases in the spin-on-glass layer that the lowtemperature cannot remove. This time period is shown in FIG. 1 in thepart of the curve marked 10.

The next part 12 of the operation curve involves ramping the temperatureat a controlled rate from the first range of temperature up to thedesired second range of temperature for curing. Control means areprovided to raise the temperature at a steady ramping rate of about 1°C./minute or more. It is important that the ramping temperature israised at the constant rate because the silicate glass tends to crackonce the stress of it bulilds up at an unacceptable rate. During therise in temperature, as indicated in the operation curve nitrogen, N₂ orArgon is started to flow into the chamber. It is flowed into the chamberstarting at this time because a convection type of heat transfor ispreferred for the curing of silicate SOG. It continues to flow into thechamber through the cooling cycle. The nitrogen or other inert gas suchas argon is flowed into the chamber at a flow rate of at least 10 sccmper minute. The ramping part 12 of the operating curve can take one ofmany curves. For example, curves A, B, and C are alternative rampingcurves. The particular curve to be used depends upon the type, whethersiloxane or silicate of sin-on-glass used and the thickness of thespin-on-glass layer or layers. For example, the A curve increases atabout 5° C. per minute and would be the curve used for siloxane type ofspin-on-glass. For silicate spin-on-glass types, the curves B and C areused depending upon the silicate type and its thickness.

The next part 14 of the operating curve is the curing of thespin-on-glass layer on each wafer timer period. The temperature of thewafer is maintained at a substantially constant level within the secondrange of temperature. The preferred temperature is between about 350° to500° C. During this curing part 14 of the operating curve is whencrosslinking of the silicate or siloxane type molecules and thesemolecules are stabilized. It is important that the vacuum continuesduring this part 14 of the operating curve, because it provides theefficient way of degassing to avoid the poison via problem in thesubsequent process steps. Even higher curing temperatures are useful ifthe metal layers in the integrated circuit is uneffected by thetemperatures. However, the usual metal used is aluminum integratedcircuits and the temperature must be limited to below about 500° C.

The final part 16 of the operating curve is the cooling period of thewafers and the chamber to between about 100° to 300° C. The means forcooling the wafer(s) to this desired temperature range may be providedby either cooling water through the heat exchanger or by using a gas,such as Helium in the gas heat exchanger.

In order to more fully understand FIG. 1, the times for the parts of thecurve 10, 12, 14 and 16 must be generally understood. The minimum timeneeded for part 10 of the curve for degassing is at least 15 minutes. Itis preferred that the time be even longer. The time, of course dependsupon the type of spin-on-glass used and the thickness of the layer orlayers. The part 12 of the curve for ramping has its ramping rate chosendepending upon the type and thickness of the spin-on-glass and itsthickness. The time needed for part 12 is decided by the temperaturedifference between the curve parts 10 and 14. The curving part 14 of thecurve should be at least 15 minutes and preferably longer. The finalpart 16 of the curve for cooling is not critical and can take whatevertime needed depending upon equipment needs.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art the various changes in form and details may bemade without departing from the spirit and scope of the invention.

What is claimed is:
 1. A vacuum degassing and curing apparatuscomprising: a chamber;means for moving at least one article to besubjected to vacuum degassing and curing into said chamber; means forproviding a vacuum of less than about 100 mtorr. in said chamber; meansfor maintaining the temperature of said article at a substantiallyconstant level within a first range of temperature during the saidvacuum degassing; means for ramping the temperature at a controlled ratefrom the said first range of temperature up to the desired second rangeof temperature for said curing; means for maintaining the temperature ofsaid article at a substantially constant level within said second rangeof temperature during the said curing; means for providing a constantinert gas flow to fill said chamber under the vacuum conditions duringoperation; and means for cooling said chamber and said article.
 2. Theapparatus of claim 1 wherein said first range of temperature is betweenabout 250° to 350° C. and said second range of temperature is betweenabout 350° to 500° C. and the maintenance of said temperature at saidconstant value is within about plus/minus 3° C.
 3. The apparatus ofclaim 1 wherein the said article is at least one semiconductor waferhaving a spin-on-glass layer thereon and said means for moving saidarticle into said chamber includes a cassette to carry said at least onewafer.
 4. The apparatus of claim 3 wherein said means for moving saidarticle into said chamber includes means for transporting a plurality ofwafers from the cassette to a quartz boat and then into said chamberwithin said quartz boat.
 5. The apparatus of claim 1 wherein said meansfor ramping the temperature at a controlled rate is at a rate of betweenabout 1° to 10° C. per minute.
 6. The apparatus of claim 1 wherein thesaid means for providing a constant inert gas flow includes a flow rateat least about 10 sccm. per minute and the gas is nitrogen.
 7. Theapparatus of claim 1 wherein the said means for cooling said chamber andarticle include passing cooling water through a heat exchanger.
 8. Avacuum degassing and curing apparatus for degassing and curing aspin-on-glass layer on a integrated circuit wafer comprising:a chamber;means for moving at least one said wafer to be subjected to vacuumdegassing and during into said chamber; means for providing a vacuum ofless than about 100 mtorr. in said chamber; means for maintaining thetemperature of said wafer at a substantially constant level within afirst range of temperature between about 250° to 350° C. during the saidvacuum degassing; means for ramping the temperature at a controlled ratefrom the said first range of temperature up to a desired second range oftemperature for said curing; means for maintaining the temperature ofsaid wafer at a substantially constant level within said second range oftemperature between about 350° to 500° C. during the said curing; meansfor providing a constant inert gas flow to fill said chamber under thevacuum conditions during operation; and, means for cooling said chamberand said wafer.
 9. The apparatus of claim 8 wherein said means formoving said article into said chamber includes means for transporting aplurality of wafers from a cassette to a quartz boat and then into saidchamber within said quartz boat.
 10. The apparatus of claim 8 whereinsaid means for ramping the temperature at a controlled rate is at a rateof between about 1° to 10° C. per minute.
 11. The apparatus of claim 8wherein the said means for providing a constant inert gas flow includesa flow rate of at least about 10 sccm per minute and the gas isnitrogen.
 12. The apparatus of claim 8 wherein the said means forcooling said chamber and article include passing Helium gas through thechamber while using cooling water through a heat exchanger.